In the context of geology and density, which type of rock layer is typically porous but must have very low to no permeability?

• A. Aquifer
• B. Reservoir rock
• C. Cap rock
• D. Aquiclude

Answer: (D)

Verified step by step guidance

1. Understand the key terms: Porosity refers to the amount of empty space within a rock that can hold fluids, while permeability refers to the ability of those fluids to flow through the rock.
2. Identify the rock types: An aquifer is a porous and permeable rock layer that can store and transmit water; a reservoir rock is similar, often storing oil or gas; a cap rock (or aquiclude) is a rock layer that is porous but has very low or no permeability, preventing fluid flow.
3. Focus on the requirement: The problem asks for a rock layer that is porous but must have very low to no permeability, meaning it can hold fluids but does not allow them to pass through easily.
4. Match the description: Since an aquiclude (cap rock) fits this description by acting as a barrier to fluid flow despite its porosity, it is the correct answer.
5. Summarize the concept: Porous but impermeable rocks (aquicludes) are crucial in geology for trapping fluids like oil, gas, or water beneath them, preventing their upward movement.